The present invention relates in general to error value calculation, and more particularly to a device, system, method and code for the calculation of systematic errors related to device testing that incorporates the accuracy of a standard""s predicted response.
The accuracy of any test is dependent on how much is known about the errors associated with the testing system. Every testing system has errors that are characteristic and unique to that system, and these errors will contaminate any test that is done. This is especially crucial for high frequency electrical devices, because systematic errors attributable to the testing apparatus can drastically alter the measured responses of a device under test (DUT). However, if the errors of a testing apparatus are constant, it is possible to determine their value. Once the value of these errors are known, it becomes possible to remove them from any subsequent measurement.
For example, to properly design and assemble electrical networks, it is critical to know the specific characteristics of the constituent devices. A vector network analyzer (VNA) is used to measure the reflection magnitude and phase of high frequency devices, and this helps designers to minimize undesirable reflections of devices and systems such as cable TV systems, telecommunication systems, and high speed computer networks. Inherent to every VNA are systematic imperfections in its measurement of device response. This means that the actual reflection magnitude and phase of a network component is different from that which is measured by a network analyzer. But because the systematic errors are constant, their value can be determined and removed from subsequent measurements.
There are many different techniques for determining the values of a testing device""s error known in the art. Likewise, there are many known methods of removing this error from subsequent measurements once the error is determined. Turning again to the VNA example, calibration, also known as accuracy enhancement, is a way to improve the measurement accuracy of a VNA measurement by measuring the responses of DUTs with known characteristics, known as standards, and comparing these measurements to the values the standards are known to produce. This is generally referred to as vector error calibration. Once the error values have been calculated, they can then be mathematically removed from the measured response of a network component. This calibration process is known in the art as vector error correction.
The present invention is directed to a system and method which provide for flexible and accurate test apparatus error value calculation. Error value calculation of a testing apparatus requires at least one unique measurement for each unknown error value using the equation that relates the measured response, the predicted response and the error value. When more equations than unknowns can be acquired, the system of equations is over-determined and an improvement of accuracy is possible. According to one embodiment of the present invention a method of testing apparatus error calculation measures a response to at least one test signal of at least one standard having a predicted response to the test signal, the predicted response having an assigned accuracy, and generates, for each standard at each test signal, an equation for determining a measurement error of a testing apparatus from at least the measured response and the predicted response, and weights the equation according to the assigned accuracy of the corresponding standard.
According another embodiment of the present invention, a device for testing apparatus error calculation has a means for producing at least one test signal, a means for measuring a response of at least one standard to the test signal, the standard having a predicted response with an assigned accuracy to the test signal, a means for generating, for each standard at each test signal, an equation for determining a measurement error of a testing apparatus from at least the measured response and said predicted response, and a means for weighting each generated equation according to the assigned accuracy of the corresponding standard.
According another embodiment of the present invention, a system for testing apparatus error calculation has an element operable to produce at least one test signal, a measurement device communicatively coupled to the element and operable to measure a response of at least one standard to the test signal, wherein at least one standard has a predicted response to the test signal, said predicted response having an assigned accuracy, logic communicatively coupled to the element and the test device operable to generate, for each standard at each test signal, an equation for a measurement error of a testing apparatus from at least the measured response and the predicted response, weighting the equation according to said assigned accuracy of the corresponding standard, and the logic further operable to solve each generated equation and calculate the measurement error using a least squares technique.
According another embodiment of the present invention, computer executable software code for calculating the measurement errors of a testing apparatus includes code operable to generate, for at least one standard at least one said test signal, an equation for a measurement error of a testing apparatus from at least a measured response of the standard and a predicted response of the standard, and weighting the equation according to an assigned accuracy of said standard; and code operable to solve each generated equation and calculate the measurement error.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.